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The Omma, Zukawa, Junicho and Yabuta Formations are typical of Plio-Pleistocene marine sediments in Hokuriku Province. The Omma and Junicho Formations have been previously dated to be early Pleistocene and late Pliocene to early Pleistocene respectively. The Takakubo Formation underlies the Omma Formation, and is dated from middle Miocene to early Pliocene.In order to establish tephrostratigraphy of the three formations (Omma, Zukawa and Junicho F.), and to make clear the stratigraphical relationship between Omma and Takakubo Formations, petrographical method, and analysis of the chemical components by energy dispersive X-ray spectrometry (EDS) were applied for the comparison of volcanic glass.As a result of this study, the following conclusions were obtained. (1) The uppermost part of the Takakubo Formation, and the lower parts of the Zukawa and Junicho Formations are in a relationship of contemporaneous heterotopic facies based on correlation of volcanic ash beds (TR 2-HK 2-SZp-T 3). (2) Based on tephrostratigraphy and biostratigraphy, the uppermost part of the Takakubo Formation is dated late Pliocene at eastern part of Kanazawa city and western part of Toyama Prefecture. (3) Between the type locality of the Omma Formation and that of the western part of Toyama Prefecture, correlation of horizons by previous biostratigraphy is inconsistent with the correlation by volcanic ash bed. 大桑, 頭川, 十二町層は北陸地域の代表的な海成の鮮新更新統である.従来の研究から, 大桑層と十二町層はそれぞれ更新世前期, 鮮新世後期から更新世前期とされている.一方, 高窪層は大桑層の下位層であり, 前期鮮新世とされている.大桑, 頭川, 十二町層の火山灰層序の確立と大桑層と高窪層との層序関係を求めるため, EDSによる火山ガラスの主成分組成測定等の検討を行った.この結果, 次のように結論づけられた.(1)火山灰層(HK 2-SZp-T 3-TR 2)の対比により, 十二町層と頭川層の最下部と高窪層の最上部は同時異相関係にある.(2)火山灰層序と従来の微化石層序から, 富山県西部地域の高窪層の最上部は鮮新世後期で, 大桑層最下部の年代に近い.(3)模式地と富山県西部地域間の大桑層において, 従来の微化石層序による対比は火山灰層による対比と斜交する

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Plio-Pleistocene tephrostratigraphy of the Omma, Zukawa and Junicho Formations and uppermost part of the Takakubo Formation in the Hokuriku Region, Central Japan.